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Limbic system & Basal Ganglia Flashcards

1
Q

What structures are in the subcortical regions of the limbic system?

A

Hippocampus, amygdala, ventral striatum/nucleus accumbens

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2
Q

What structures are in the cortical regions of the limbic system?

A

Prefrontal, cingulate, insula, parahippocampal gyrus

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3
Q

What is the neuromodulatory pathway to the cortex involving NE and what does it control?

A

Projection from locus ceruleus (in pons) to cortex, brainstem, spinal cord, cerebellum (everywhere)
Attentional selectivity under stress

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4
Q

What is the neuromodulatory pathway to the cortex and basal ganglia involving DA and what does it control?

A

Projection from ventral tegmentum (midbrain) to prefrontal cortex and basal ganglia
PFC projection promotes motivationally based behavior

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5
Q

What is the neuromodulatory pathway to cortical areas via serotonin and what does it do?

A

From raphe nucleus (medulla)

Mood; sleep-wake cycles

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6
Q

What is the neuromodulatory pathway to thalamus and extensive cortical areas via Ach and what does it do?

A

from Septum, nucleus basalis, diagonal band of Broca

Facilitate hippocampal and other cortical regions in memory and cognition

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7
Q

Where is the hippocampus?

A

3 layers near the surface of medial temporal lobe, bulges into lateral ventricle

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8
Q

What afferent connections does the hippocampus have?

A

Afferents go into cortex (sensory, association, cingulate and PFC)–>parahippocampal gyrus in temporal lobe–>entorhinal cortex–>hippocampus

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9
Q

What are the functions of the hippocampus?

A

Encodes and consolidates episodic memories and projects to wide areas of cortex
Combines information from both ventral (what) stream and dorsal (where) stream to form episodic memories

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10
Q

What efferent connections does the hippocampus have?

A

Efferents opposite from afferents

Contextual information is consolidated as memory into wide areas of cortex: prefrontal, temporal, parietal

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11
Q

What is declarative memory?

A

Declarative memory: episodic (short-term context) and semantic (long-term, concepts)

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12
Q

What is the role of the hippocampus and vmPFC in forming and consolidating declarative memory?

A

I don’t know

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13
Q

What are the stages of sleep and their EEG correlates?

A

REM: similar to waking, low amplitude, high frequency, 2nd half of sleep
non-REM: stages 1-4 increase in amplitude, decrease frequency, slow wave sleep (SWS), 1st half of sleep

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14
Q

What are the pathways that maintain wakefulness, and how do you fall asleep?

A

Ascending reticular pathways from brainstem to thalamus: cholinergic pontine pathways
From brainstem to cortex: monoaminergic pathways (NE, serotonin, DA), Cholinergic pathway from basal forebrain nucleus , orexin pathway from lateral hypothalamus

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15
Q

How is sleep regulated by a circadian rhythm?

A

SCN projects light-dark phases to dorsal medial nuclei of hypothalamus (DMH)
With light, DMH promotes wakefulness by inhibiting VLPO (ventrolateral preoptic nucleus)
Cytokines (TNF, IL) disrupt the circadian sleep cycle during illness permitting sleep during the day for recovery

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16
Q

How is memory consolidated in sleep?

A

Early nocturnal sleep (SWS stages 2-4): consolidate declarative and procedural memory
Late nocturnal sleep (REM): Final consolidation of memory

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17
Q

When does the reactivation of memory occur in sleep? When are they consolidated?

A

Declarative memories encoded by hippocampus are reactivated during SWS via decrease in ACh during SWS
Consolidated in several cortical areas for permanent storage during SWS and REM (enable insight from multiple similar episodes)

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18
Q

What role does the septum have in ACh’s effect on cortical memory?

A

Septum regulates memory encoding in hippocampus via theta rhythms that separate periods of encoding of sensory stimuli and retrieval of episodic memory to avoid interference

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19
Q

What role does the diagonal band of Broca have in memory consolidation?

A

Nucleus basalis of Meynert (AKA band of Broca) projects to neocortex to facilitate in memory consolidation
Degenerates in Alzheimer’s

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20
Q

What sleep-wake conditions optimize memory consolidation?

A

Memory reactivation during SWS mostly

REM sleep consolidation enables insight and correlations across multiple similar memories

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21
Q

How is memory consolidation affected in Alzheimer’s disease?

A 
Inability to consolidate short term to long term memories
Nucleus basalis (Meynert) degenerates, leading to cognitive deficits, beta-amyloid plaque (extracellular)
Degeneration of cortex, cholinergic tracts
Neurofibrillary tangles (intracellular)
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22
Q

How is memory consolidation affected in bilateral hippocampectomy?

A

Loss of memory consolidation

Only long term memory present (know how to lift a cup up but don’t remember what happened 1 minute ago)

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23
Q

How are emotional experiences manifested?

A

ANS: physiological, visceral
Behaviors: facial expressions
Subjective feelings: love, fear, hate

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24
Q

What role does the amygdala play in expressing emotions?

A

Take cognitive-emotion interactions and consolidate into memory (associate things with how you feel about them)
Perception and attention to both emotional valency (positive, negative) and intensity of personal and interpersonal emotions (with cortex)

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25
How do the efferent pathways from the amygdala generate affective/emotional attention?
Descending projection: go through hypothalamus which controls ANS for affective significance Amygdala mediates expression of innate and learned fear, and anxiety Increased heart rate, respiration, urination changes
26
What types of facial expressions do the amygdala respond to and why?
Ambiguity: responds less to angry faces but more to fearful or surprised faces Reacts more via fear to something you think might be danger
27
What is emotional memory?
Conditioned fear via amygdala
28
Describe conditioned fear and extinction and what brain areas generate them.
Conditioned fear is when sensory cues acquire significance via classical or Pavlovian conditioning CS-US coupling of a sound and electric shock in quick sequence can generate amygdalar responses
29
How is the amygdala regulated in its expression of emotional responses?
mPFC regulates the expression of emotions while hippocampus provides context to distinguish differences in threat
30
What does it mean that the amygdala retrieves emotional memories unconsciously?
Masking of an emotional face (fearful, angry) within 15 ms doesn't inhibit conditioned ANS response Unconscious retrieval is mediated by auditory and visual association cortices, anterior insula, fusiform gyrus, pulvinar nucleus (subconscious pathway)
31
Compare memories of emotions vs emotional memories.
Implicit emotional memories: Amygdala expresses emotions Explicit memories about emotions: Hippocampus forms cognitive semantic and episodic representations of emotional situations that have happened
32
How do high levels of NE and DA neuromodulation affect the relationship of prefrontal cortex and amygdala?
High NE and DA in response to stress inhibit PFC effects on amygdala, impairing working memory and attention, and strengthening fear conditioning in amygdala leading to anxiety
33
What is meant by top-down and bottom-up control of the amygdala?
Top-down: PFC control, overrides compulsive behavior, slow, thoughtful regulation Bottom-up: Sensory cortices, high NA, amygdala action especially during high stress, biasing toward habitual motor responses, reflexive emotional responses
34
What effects do lesions of the vmPFC/OFC have on behavior?
Disinhibit amygdala Unable to plan ahead, recognize consequences of actions Inhibit emotional tendencies (Phineas Gage - aggressive)
35
What effects do lesions of the amygdala have on behavior?
Inability to link past experiences to stimuli with important behavioral consequences Don't care about dangerous snake Less aggression Inappropriate sexual behavior Inability to recognize facial expressions of strong emotions, especially fear Visual, auditory or tactile agnosia
36
Describe the location and some of the functions of the insula.
Deep to temporal lobe Sends info to amygdala Cue-processing (posterior) "what" and "where is it" Context processing (anterior) "snake in a box" versus "snake in the wild"
37
How does the insula relate to the amygdala?
In anxiety, amygdala has unconscious anticipatory reactivity while insula has conscious enhanced response to neutral stimulus when paired with aversive stimulus Insula is stimulated by amygdala during negative states such as perceiving fearful faces, threat, expectation of painful stimuli Interoceptive state: anxious individuals have an exaggerated prediction signal of a prospective aversive body state
38
What is working memory?
Maintain and update task-relevant representations in mind; mental sketch pad; less dependence on environmental cues; activation of prefrontal and inferotemporal areas during delay of remembering a face
39
What does the dlPFC do in working memory?
Executive control functions: formulate goals, inhibit inappropriate emotions, impulses, habits, conscious awareness, anticipate events in the near future
40
What is the significance of the prefrontal cortex’s ability to sustain activity over long periods of time?
Working memory is sustained by NE and DA in dlPFC; strong connections to other parts of the brain to sustain attention
41
What is the role of NE and DA in maintaining working memory? What happens in the dlPFC if there is excess of NE and DA?
NE and DA have complementary actions on dlPFC neurons: NE increases signals to preferred inputs, DA decreases responsivity to non-preferred stimuli Excess = everything suppressed (a1) Optimal (a2)
42
What is basal ganglia?
Gray matter in the cerebral hemisphere that surround the thalamus
43
What are the major constituents of the basal ganglia?
``` Caudate Putamen nucleus accumbens globus pallidus subthalamic nucleus substantia nigra, VTA ```
44
What is the striatum?
Caudate plus putamen
45
Where is the caudate and putamen?
caudate has head body and tail surrounding thalamus - nucleus accumbens at anterior of the head Putamen separate from caudate by internal capsule passing between cell bridges
46
Where is the globus pallidus?
GPi and GPe are medial to the putamen (thalamus even more medial), look like lens in lateral view
47
Where is the subthalamus?
It is in between the globus pallidus and midbrain
48
Where is the substantia nigra?
Midbrain
49
What is a corticostriate (CS) loop?
motor/cognitive cortical info goes through striatum and globus pallidus Globus pallidus projects to thalamus which in turn conveys info back to frontal cortex to refine motor and cognitive plan Substantia nigra and subthalamus modulates loop
50
What is the direct and indirect pathways of the CS loops?
Selection of direct pathway - excitatory effects via striatum--/GPi--/Thalamus-->Increased motor output Indirect pathway - inhibitory effects via striatum--/GPe--/subthalamus-->GPi--/Thalamus-->decreased motor output
51
How does the direct and indirect pathway affect intended movements?
Direct path permits intended movements | Indirect path inhibits unintended movements
52
How does DA neuromodulate the striatum?
It acts in reinforcing direct and indirect pathways to determine preferred strategies Persistent reinforcing stimuli (S-R) conditioning permits striatal pathway activity without need for DA, no longer outcome mediated because it's become habit
53
What receptors do DA use in reinforcing direct and indirect pathways?
DA activates direct pathway via D1 type DA receptors Inhibits indirect pathway via D2 type DA receptors DA enhances strong inputs; suppresses weak ones Internally generated behaviors reinforced by DA become habitual
54
Name the four CS loops.
Visual Motivational Executive Motor/premotor
55
What parts of the cortex do each of the four CS loops involve?
Visual - temporal/ventrolateral prefrontal (externally generated actions) Motivational - orbitofrontal/anterior cingulate Executive - dorsolateral prefrontal/posterior parietal Motor - premotor/SMA/somatosensory (internally generated actions)
56
What are the general functions of each of the four CS loops?
They all converge someplace on striatum; motivational loop sends episodic memory to executive loop, which in turn sends input to motor loop for appropriate actions
57
What is declarative memory?
Hippocampus-limbic events where episodic memories are stimulus-stimulus associations consolidated into semantic memory in cortex
58
What is emotional memory?
Amygdala - emotional conditioning by association of stimulus and aversion
59
What is procedural (non-declarative) memory?
``` Cerebellum (precise motor) and basal ganglia (habits) - based on associating motor responses with reinforcing stimuli (S-R) to build a repertoire of motor actions i.e. driving Unconscious rigid procedural ```
60
What are the three aspects of procedural memory pertaining to the CS loops?
Category representation - stimulus from sensory association cortex are linked to appropriate behaviors by clustering similar categories together Action selection - loops select for desired motor response Instrumental and reward learning - conditioning behavior to new cognitive or emotional cues reinforced by DA
61
What is declarative learning of visual categories?
Declarative - relevant info is maintained over time in working memory, memories are compositional and can be separated, flexible to change memory upon retrieval of new information Hippocampus, vmPFC, dlPFC
62
What is procedural learning of visual categories?
Complex info, associated with behavioral responses, related elements are unified, less flexible Loop branches to executive and premotor loops, integrate with executive control and working memory
63
What impact does DA neuromodulation have in action selection?
Phasic DA activity reinforces specific actions or shifts loops from one action to another depending on feedback from DA system Forms goal-oriented activity i.e. learn how to ride a new bike
64
What impact does DA have in instrumental/reward learning?
Procedural learning occurs with shift from goal-oriented action (kick) to a stimulus-response (see ball) association, and behavior becomes inflexible, habit Extinction of inappropriate learned responses uses switching of strategies (DA no longer reinforces pathway)
65
What is instrumental learning?
Stages: naive (processing through basal ganglia is undifferentiated) Appropriate (corticostriatal learning reinforced by DA, task-related elements are sharpened) Aberrant learning (inappropriate plasticity in the indirect pathway induces inappropriate inhibition and facilitation, task-related elements are noisy)
66
What is reward learning?
Goal-oriented behavior subject to motivational state Associate stimulus with reward rather than motor response based on memories in orbitofrontal and mPFC Affective experience: sight of food, anticipation that it will be good; taste, smell also cues for reinforcement of behavior
67
What are the characteristics and causes of Huntington's chorea?
Involuntary jerky movements of face, tongue, limbs Due to lesion of striatum and cortex, causing underactivity of indirect path and facilitating direct path Loss of striatal GABA neurons that project to GP, AD disease
68
What are the characteristics and causes of athetosis?
Writhing limbs | Same loss of striatal GABA neurons seen in chorea
69
What are the characteristics and causes of hemiballismus?
Flailing of limbs | Lesion of subthalamus (from virus) reduces inhibitory control over thalamus and cortical output
70
What are the characteristics and causes of Parkinson's disease?
Rest tremor, rigidity, inability to switch strategies, bradykinesia (slow motion) Due to degeneration of pigmented DA neurons in substantia nigra, less DA to dorsal and ventral striatum
71
What is the imbalance among the limbic regions in schizophrenia?
Excess hippocampal activity generates excess tonic levels of DA onto the NAc via ventral pallidum (VTA pathway) GABA is dysregulated More tonic DA inhibits PFC input into NAc, more responsive to extraneous stimuli
72
What are the general actions of addictive drugs on the motivational CS loop?
Addictive drugs reinforce behavior by increasing DA levels via: inhibiting uptake or increasing release in the accumbens, inhibiting GABA inhibition in VTA, stimulating nicotinic cholinergic receptors in VT DA cells DA release leads to neuronal plasticity that may underlie incentive learning and long-term memories associated with cravings in addiction

Organ Systems (5 decks)

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